Automatic volume control



012L130, 1934. w RUNGE 1,978,552

' AUTOMATIC VOLUME CONTROL Filed Feb. 9, 1955 w 5/. Ill/M745; 452242225 INVENTOR WlLHELM RUNGE BY WQZM ATTORNEY Patented Got.

PATENT OFFICE s 1,978,552 AUTOMATIC VOLUME CONTROL Wilhelm Runge, Berlin, Germany, assignor to Telefunken Gesellscliaft fiir Drahtlo'se Telegraphie' in. b. EL, Berlin, Germany, a corporation er Germany Application February 9, 1933, serialize. 655,888 I In Germany February 13,;1932

4'Claims. -(c1. 179-171) The present invention relates to an arrange ment .for automatic volume control of receivers.

It'isknown to secure an automatic volume control of a receiver by rectifying the amplitude of the high frequency carrier, and toaproduce a voltage drop: across a resistance with the direct current component thus produced, and apply the component as' an additional grid bias to one, or severahamplifying stages ahead of this rectifier.

For battery heated tubes in which large direct current resistances cannot possibly be arranged in the cathode circuit between battery and filament, these automatic volume control systems always require a considerable amount of addilj ltional equipment (separate batteries, additional rectifier tubes and the like).

In the following an illustrative circuit is described which is suited for many purposes. This circuit is based upon the principle of automatic ,ijtlolume control, and operates so as to limit the maximum audio frequency amplitude of the re ioi' the last tube.

ceiver and needs only a few additional circuit elements.

The novel features which I believe to be charfibcteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation being best understood by reference to the following description taken in iconnection with the drawing, in which I have indicated diagrammatically one circuit arrangement whereby my invention may be carried into efiect.

The circuit is shown in the accompanying frlrawing, in which it is assumed that the receiver includes a two stage audio frequency amplifier. The power tube 1 instead of a separate grid bias, has a parallel arrangement of the condenser 2 and a resistance 3 inserted in the grid lead. Whenever an amplitude of the alternating potential is "is greater than that of the precedingtube 6, or

if a higher anode potential is applied to the power tube, the throughgrip of the power tubes and the preceding tubes being equal, a grid bias placing the power tube just to its working point, produces a biasing of the pre- ...cieding tube at its lower bend; below which the never appreciably increase beyond this value.

amplification oi the tube'decreases considerably. The amplitude of the power tube, therefore, can In order to prevent voltage variations, produced at the condenser 2 during rectification from entering into the preceding stage causing thereby an undesiredreturn coupling, the preceding stages may be tie-coupled against the short voltagevariations,.for instance bymeans of the resistance 4 and the condenser 5 which serve for applying the direct current potential component of the grid bias to the preceding tube while considerably decreasing the alternating current potential component.

This method is particularly suited for transmitting messages with a substantially constant degree of modulation, as in the case of commercial telephony, since it maintains the low frequency output volume constant, and accordingly, compensates for the variations of the degree of modulation in accordance with variations of volume. (difference between piano and forte of musical sounds). Moreover the importance of this method resides in the simplicity and cheapness of the means employed.

, While I have indicated and described one circuit arrangement for carrying my invention into effect it will be apparent to one skilled in the art that my invenion is by no means limited to the particular circuit shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What is claimed is- 1. In a radio receiver, an audio amplifier network including a power output tube, a preceding audio amplifier tube having its output circuit coupled to the input circuit of the power tube, a resistor-condenser arrangement in the grid circuit of said power tube for developing a direct current voltage from grid current flow in said grid circuit, a direct current comiection between the grid circuit of said preceding tube and said arrangement whereby said voltage is used to bias the grid of said preceding tube, the tube constants of said preceding tube and power tube being such that grid bias placing the power tube just to its working point produces a biasing of the preceding tube to the lower bend of its characteristic.

2. In a radio receiver, an audio amplifier network including a power output tube, a preceding audio amplifier tube having its output circuit coupled to the input circuit of the power tube, a resistor-condenser arrangement in the grid, circuit of said power tube for developing a direct current voltage from grid current flow in said grid grid of said preceding tube, means in the grid circuit of said preceding tube for substantially decreasing the alternating potential developed across said arrangement and fed through said direct current connection, the tube constants of said preceding tube and power tube being such that a grid bias placing the power tube just to its working point produces a biasing of the preceding tube to the lower bend of its characteristic.

3. In a radio receiver including an audio amplifier system having a power output tube and at least one preceding audio amplifier tube, an arrangement for compensating for the variations of the degree of modulation in accordance with variations of volume comprising a resistor-condenser network in the grid circuit of the power tube for developing a direct current voltage from grid current flow in said grid circuit, a direct current connection between a point of negative potential on said resistor and the grid circuit of said preceding tube whereby the negative bias for the preceding tube grid is provided by said voltage, and the amplification factor of said power tube being sufficiently higher than that of the preceding tube to prevent the grid bias of said power tube from appreciably increasing beyond that value required to operate the power tube at its Working point.

4. In a radio receiver including an audio amplifier system having a power output tube and at least one preceding audio amplifier tube, an arrangement for compensating for the variations of the degree of modulation in accordance with variations of volume comprising a resistor-condenser network in the grid circuit of the power tube for developing a direct current voltage from grid current flow in said grid circuit, a direct current connection between a point of negative potential on said resistor and the grid circuit of said preceding tube whereby the negative bias for the preceding tube grid is provided by said voltage, the amplification factors of both tubes being equal, and the anode potential of said power tube being sufficiently higher than that of the preceding tube to prevent the grid bias of said power tube from appreciably increasing beyond that value required to operate the power tube at its working point.

WILHELM RUNGE. 

